You can only have one chat window open at any time. You've been logged out of chat because one more person has accessed chat under your account. It might be you opening another chat window or your partner trying to access chat on another computer. If you think that someone else is accessing your chat account on another computer without your permission you should change your password.
If you're a couple and enjoy using chat together on different computers you can register another account and make it clear it's a secondary account for chat use.
Don't forget, site supporters can dock multiple cams and view enlarged cam.